Surface-plate.



W. C. COMMONS.

SURFACE PLATE.

' APPLICATION FILED FEB. 17. 1915.

11 Patented Oct. 26, 1915.

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WILLIAM C. COMMONS, OF WOONSOCKET, RHODE ISLAND, ASSIGNOR TO TAFT PEIRCEMANUFACTURING COMPANY, OF WOONSOCKET, RHODE ISLAND. A COR- IPOBATION OFRHODE ISLAND.

SURFACE-PLATE.

Specification of Letters Patent.

Patented @ct. 26, 31915.

To all whom it may concern:

Be it known that I, WILLIAM C. COMMONS, a citizen of the United States,and a resident of the city of Noonsocket, in the county of Providence,State of Rhode Island, have in vented new and useful Improvements inSurface-Plates, of which the following is a specification.

This invention relates broadly to tools and more particularly toprecision tools in the nature of surface plates.

The principal object of this invention s to provide a surface plate ofextremely rigid construction having the test surface thereon supportedby members adapted to absorb and distribute any stress applied to saidsurface. I

A further and primary object of this 1nvention is to provide a surfaceplate with a test surface so constructed as to minimize A thepossibility of error due to collection of foreign matter on the saidsurface,

A further object of this invention is to provide a surface plate with atest surface constructed of a plurality of small spaced test surfacesall of which lie in the same plane.

Another object of this invention is to pro vide a surface plate with atest surface constructed with depressions adapted to collect and receiveforeign matter, such as dirt and grit which may accidentally bedeposited on said'surface.

A still further object of this invention is to produce a surface platehaving a test surface thereonconstructed to obviate the production ofvacuums between the test surface and the work being tested thereon.

Other and further objects of this invention will in part be obvious andwill in part be pointed out hereinafter byreference to the accompanyingdrawings wherein like characters are used to represent like partsthroughout the several figures thereof.

Figure 1 is a plan view. Fig. 2 is an elevational view showing a portionof the device in section. Fig. 3 is a small detail view illustrating asmall section through the test surface. Fig. ?l is a plan view lookingat the bottom of the device.

Surface plates are old and well known devices used in precision toolwork, and are usually constructed with surfaces which are scraped to liein substantially a single plane.

These surfaces as heretofore produced are usually of relatively largearea. In the use of such surface plates it is customary to coat theplate with a very thin layer of red lead or some oily substance andapply the work to be tested to the coated surface. Where the work facebeing tested has a rela tively large area, the application of the workface against the test surface expels substantially all of the airbetween the two surfaces. Any attempt to separate the surfaces has theeffect of producing a vacuum and the surfaces are held together byatmospheric pressure. It will be seen that where the surfaces arerelatively large the effective atmospheric pressure is considerable, andconsequently the test surface of a surface plate is often injured inattempting to remove tested work from the said surface. In the surfaceplates heretofore produced, having large test areas, it was necessary tocarry grit or dirt which might lodge in the center of the plate entirelyto the edge of the plate before it could be removed from the testsurface. As these test surfaces are substantially true planes it will beseen that the continual wiping of grit and dirt across the surfaces willin time appreciably affect their accuracy.

The present invention which will hereinafter be described by referenceto the drawings, includes a surface plate having a relatively large testsurface composed of a great number of small surfaces separated bydepressions or grooves. It will immediately be seen that these groovesat all times admit atmospheric pressure between the work and the generalarea of the testsurface thereby obviating the liability of sticking dueto atmospheric pressure. It also breaks up the test surface into smallareas and thereby substantially obviates adhesion. It will also be seenthat by having the test surface made up of relatively small areasseparated by grooves that any particles of dust or dirt need only becarried a very short distance before they are disposed of, by lodging inone of the grooves. This type of surface plate therefore is extremelyaccurate, due to the elimination of possible errors from the causesspecified, and is very durable and not liable to injury due to sticking.Furthermore, the surface plate forming the subject of the presentinvention includes a relatively thick plate of metal idity for the leastamount of metal.

Referring now more particularly to the drawings, the bed plate 1 isprovided with an accurately formed test surface 2. This surface may beformed by grinding, lapping, or any other well known method of producingaccurate surfaces. This test sur face is cut by a plurality ofintersecting grooves 42 thereby dividing the general surface 2 into amultitude of small surfaces 5. These small surfaces all lie in the sameplane, and therefore effectively cooperate in such manner as'to beequally as useful as a test plane as if the grooves a were absent. Ashas been previously explained, the grooves 4i obviate sticking andafford lodging places for foreign matter, thereby minimizing thepossibility of error due to these two causes and also increasing theeffective life of the test surface; Since the use of the test surfacenecessarily demands that it be supported so that it will not tend tobend or twist when in use, the present in vention includes a very rigidbacking or support which comprises a pair of large intersectingtriangles A and B arranged so that the apex of triangle A substantiallybisects the triangle B, and vice versa. A web C joins the intersectionof the sides of the triangles A and B, thereby forming substantially sixsmall nested triangles 6. In order to take advantage of the cantalivereffect in securing rigidity and absorption of stresses, the majortriangles A and B are slightly smaller in their dimensions than is thearea of the bed plate 1, and the overhanging parts of said bed plate aresupported at the ends by brackets 7 extending substantially parallel tothe length of the bed plate, and the sides are also supported bybrackets 8 extending substantially transverse of the bed plate. In orderto produce an even primary support for said plate, supporting feet 9 arepreferably formed at each angle of the triangle B thereby providing athree point suspension or support for Copies of this patent may beobtained for the plate to be carried upon. Bosses 10 are formed adjacentthe meeting of the central bracket 7 and the bed plate 1, and preferablyare threaded to receive the lifter bolts or handles 11, which may beused in lifting the plate where the work is of such a nature that it isdifficult to bring the work to the plate, in which case the plate islifted and applied to the work surface.

By reference to Fig. 2 it will be noted that the webs are thinner insubstantially the transverse middle portion of the supporting members,and this construction is of utility for two reasons; first, the basewebs of the triangles A and B act substantially as cantalivers so thatfor supporting purposes the metal may be lessened at the middle of thewebs, and secondly this construction permits of a free air circulationbeneath the bed plate and the supporting members thus i11- suring theplate to be subjected to substantially the same temperature conditionson all sides thereof. This feature is of considerable importance, as onrelatively large surface plates, unequal heating may have a tendency tovery slightly warp or bend the plate thus introducing an error which maybe appreciable in extremely accurate work.

Having thus described my invention'what I desire to claim is 1-- 1. Asan article ofmanufacture, a surface plate having the test surfacethereof crossed by a plurality of grooves.

2. As an article of manufacture, a surface plate having the test surfacethereof crossed by a plurality of intersecting grooves to divide saidtest surface into a plurality of individualized areas.

3. As an article of manufacture, a surface plate having a test surfaceprovided with a plurality of depressions adapted to collect and receivegrit and dirt.

4. As an article of manufacture, a surface plate having the test surfacethereof crossed by a plurality of intersecting straight line grooves.

WILLIAM G. COMMONS.

Washington, I). C.-

